Dynamic multiplier



June 2, 1936. M JR 2,042,988

DYNAMIC MULTIPLIER Filed Feb. 15, 1935 INVENTOR ATTQRNEYS Patented June2, 1936 UNITED STATES PATENT OFFICE DYNAMIC MULTIPLIEB John HaysHammond, In, Gloucester, Mass. Application February 15, 1933, Serial No.656,814

11 Claims. (CL 179-1001) This invention relates to amplifying systemsand more particularly to an improved method of controlling the amount ofamplification in accordance with the strength of the applied energy.

The invention relates particularly to a system of amplification in whicha greater ratio of amplification or gain is produced for impressedsignals of high intensity than for impressed signals of low intensitywhereby the volume range of the signal is expanded.

The present invention provides for controlling the operatingcharacteristics of sound reproducing or recording devices in accordancewith the strength of the applied signal. As applied to an 1-5electromagnetic reproducing or recording device the invention providesfor varying the field strength of the device according to the generalenergy level of the signal so as to produce relatively more response toloud signals than to weak.

signals whereby the sound range of said device is expanded.

The invention also consists in certain new and original features ofconstruction and combinations of parts hereinafter set forth andclaimed. 25 Although the novel features which are believed to becharacteristic of this invention will be particularly pointed out in theclaims appended hereto, the invention itself, as to its objects andadvantages, the mode of its operation and the 3o manner of itsorganization may be better understood by referring to the followingdescription taken in connection with the accompanying drawing forming apart thereof, in which The figure illustrates diagrammatically the 35system as applied to the reproduction of the sound record of either atalking moving picture film or a phonograph record, or to the recordingof a sound record.

In the following description and in the claims, parts will be identifiedby specific names for convenience, but they are intended to be asgeneric in their application to similar parts as the art will permit.

Referring more particularly to the drawing a 5 light source' III isprovided, the light from which is focused by a lens II through anaperture I2 in an aperture plate I3 and upon the sound record of amoving photographic film I4. The light which pa'sses'through this filmis focused by a 50 second lens I5 upon a photoelectric cell I5. Thiscell is connected through a battery H to the primary of a transformer I3the secondary of which is connected in the input circuit of a spacedischarge amplifier I9 of well known form. The 55 output circuit of thisamplifier includes the primary of a transformer 2I, one side of thesecondary of which is connected to one contact I2I of a three positionswitch 22.

A phonographic pick-up device 23 for use with a disc record is provided,which includes an ar- 5 mature coil I23 and a field coil I24. One sideof the armature coil I23'is connected to the second contact I of theswitch 22.

A microphone I26 is provided for sound recording purposes and isconnected to the primary of 10 a transformer I21. ,One side of thesecondary of this transformer is connected to the third contact I28 ofthe switch 22.

The blade of the switch 22 is connected to the grid of a space dischargedevice 24, the cathode 16 of which is connected through a biasing,battery 28 to the other side of the armature coil I23 of the phonographpick-up 23, and to the other sides of the secondaries of thetransformers 2| and I2'I.

The output circuit of the device 24 includes the 20 primary of atransformer 25 the secondary of which is connected across apotentiometer. 26. The adjustable contact of the potentiometer 25 isconnected to the grid of a space discharge de-, vice 21, the devices 24and 21 being provided with 25 a common biasing battery 28, filamentbattery 23, and plate battery 30.

The output circuit of the device 2'Iis connected to the primary of atransformer 32, the secondary of which is connected to the input circuitof a push-pull amplifier 33. The output circuit of this amplifier 33 isconnected to the primary of a transformer 34 provided with twosecondaries 35 and 33. The secondary 35 is alternately connected bymeans of a single pole double throw 35 switch I35 to the armature coil31 of a loud speaker 38 of well known form, and to the armature coil I35of a phonographic engraving tool I31, which is also provided with afield coil I38.

The secondary 35 is connected in a circuit in- 40 eluding tworesistances H and 42, and a rectifier 43 which permits current to fiowin resistance 42 in the direction of the arrow. The resistance 42 may beshunted by a condenser 44 adapted to control the time characteristics ofthe current 45 flowing therein. The resistance 42 is connected in theinput circuit of a space discharge device .45 to control the biasingpotential of the device 45 according to the potential drop across saidresistance 42. The connection is shown as such so that an increase incurrent in resistance 42 increases the negative biasing potential on thedevice 45 and thereby reduces the current in the plate circuit thereof.The output circuit of space discharge device 45 includes a secondarywinding 48 of a transformer 41, the primary of which is connected to asource of A. C. supply 5i, and a resistance 48 shunted by a condenser49. The secondary 48 constitutes a source of plate current for thedevice 45. The resistance 48 is connected in parallel in the inputcircuits of two space discharge devices 52 and 53 and determines thebiasing potential thereon. The filaments of the devices 45, 52 and 53are heated by current from a secondary winding 54 of the transformer 41.

The plates of the devices 52 and 53 are connected across a secondarywinding 55 of the transformer 41 which serves as a source of spacecurrent therefor and to the field winding 58 of the loud speaker 38 andthe field winding I38 of the engraving tool I31, in parallel. The returnleads of the field windings 56 and I38 are connected to the mid-point ofthe secondary 54. A condenser 51 may be shunted across the field winding58 to control the operating characteristics of the loud speaker 38.

The field winding I24 of the phonograph pickup 23 is selectivelyconnected by a single pole, double throw switch 54 to a battery 62 or,in parallel with the field winding 58, in the output circuit of spacedischarge devices 52 and 53. A variable resistance 5i may be included incircuit with the winding I24 to control the energization thereof.

In the operation of the above described system the switch 22 is throwninto engagement with the contact I2I when it is desired to use the soundfilm I4. When it is desired to use the phonograph pick-up 23 the switch22 is thrown into engagement with the contact I25 and when it is desiredto use the microphone I25 it is thrown into engagement with the contactI28. In any case sound energy from one of these sources is fed to theinput circuit of the space discharge amplifier 24, where it is amplifiedand fed through the transformer 25 to the space discharge device 21.Here it is further amplified and fed through the transformer 32 to thepushpull amplifier 33. A large part of the output of this amplifierpasses through the secondary 35 to the armature coil I35 of theengraving tool I31, or to the coil,31 of the loud speaker 38, dependingon the position of the switch I35. The rest of the energy passes to thecontrol circuit through the secondary 38 and causes current to fiowthrough the resistance 42 in the direction of the arrow.

When no signal is being received, no current will fiow through theresistance 42 and therefore no negative potential will be applied to thegrid of the device 45. Under these conditions'the device 45 is adaptedto pass a large pulsating current through the resistance 48 in thedirection of the arrow, thereby building up a large negative potentialon the grids of the devices 52 and 53 adapted to increase the impedancethereof so as to reduce the current fiowing in the output circuitincluding field winding 55 or I38. Therefore the volume of sound emittedby the loud speaker 38 or the energy recorded by the tool I31 will be ata minimum. Condenser 44 controls the operating time characteristics ofthe control circuit so that the control is responsive to the averageenergy level of the sound responsive means over a predetermined intervalof time corresponding to, for example, the rate of change in sound levelas distinguished from the instantaneous energy level of the sound waves.

When a large signal is received the current flowing through theresistance 42 will be large and a high negative potential will beapplied to the grid of the device 45, thus increasing its impedance andcutting down the current flowing through this device and through theresistance 5 48. This will decrease the negative potential applied tothe grids of the devices 52 and 53, thus allowing these devices to passa large amount of current which will flow through the field windings 58or I38 and increase the volume of sound 10 emitted by the loud speaker38 or the energy recorded by the engraving tool I31.

With the switch down (in the arrangement illustrated), part of thecurrent from the devices 52 and 53 will flow through the field winding15 I24 of the phonograph pick-up 23. When the input signal is weak thiscurrent will be small, so that the magnetic flux of the pick-up 23 willbe low. The currents induced in the armature winding I23 of this devicewill, therefore, be 20 decreased, thus decreasing the input energy tothe amplifier 24 which will still further reduce the volume of soundproduced by the loud speaker 38.

When the input signal is strong, a large amount 5 of current will flowthrough the winding I24, thus increasing the magnetic flux produced,which in turn will increase the currents flowing through the armaturewinding I23 of the pick-up 23. This will increase the input energy tothe amplifier 24, thus increasing the energy fed to the armature coil 31of the loud speaker 38, thereby further increasing the volume of soundproduced by this device.

If it is desired to use the pick-up 23 in a standard manner, the switch64 is thrown to the up position, thus connecting the battery 62 acrossthe field I24 and thereby producing a constant magnetic flux in thefield of this device.

It is thus seen that this system provides a a means whereby the volumeof sound emitted by the loud speaker 38 or recorded by the engravingtool I 31 is less on weak signals and greater on strong signals than itwould be if the field windings of the loud speaker 38 and engraving toolI31 were uniformly energized by a constant field current. In this way itis possible to increase the dynamic range of the loud speaker or therecording device.

It is also possible to increase this range by controlling the magneticflux of the pick-up device, thus producing a regenerative action whichgreatly increases the strength of the strong signals and decreases thestrength of the weak signals.

It is to be understood that the loud speaker 38 or the engraving toolI31 are illustrative only and may be replaced by any suitable and wellknown device for recording sound, for example, on a moving photographicfilm or the like. 0

Although onlyone of the various forms in which this invention may beembodied has been shown herein, it is to be understood that theinvention is not to be limited to any specific construction, but may beembodied in various forms 5 without departing from the spirit of theinvention or the scope of the appended claims.

What is claimed is:

1. In a sound translating system, means responsive to sound energy,amplifying means adapted to amplify said sound energy, a soundreproducing device, a sound recording device, means to actuate either ofsaid devices in accordance with the instantaneous value of saidamplified energy and means to modify the actuation aosapaa I v thereofin accordance with the average value of said energy over a predeterminedtime interval.

2. In a sound record system. input means. responsive to sound energy,translating means actuated thereby, an output'device actuated by saidtranslating means, and means controlled by the average energy level tovary the response characteristics both of said input means and of saidoutput device.

3. In a sound record system, means responsive to sound energy adapted totranslate said soimd energy into electrical energy, a space dischargeamplifier therefor, a utility responsive to said electrical energy, saidutility having a variable magnetic field adaptedto control-its responsecharacteristics, and means to energize said field in accordance with theaverage level of said sound energy over a predetermined time intervaland an independent source of space energy for said amplifier.

4. In a sound record system, means responsive to sound energy adapted totranslate said sound energy into electrical energy, a space dischargeamplifier therefor, a utility responsive to said electrical energy, saidutility having a variable magnetic field adapted to control its responsecharacteristics, a source of energizing current for vsaid field, andmeans to control said current in accordance with the average value ofsaid electrical energy over predetermined time intervals and anindependent source of space energy for said amplifier.

5. In a sound record system, means responsive to sound energy adapted totranslate said sound energy into electrical energy, a space dischargeamplifier therefor, a utility responsive to said electrical energy, saidutility having a variable magnetic field adapted to control its r sp nsecharacteristics, an energizing winding for said field, a space dischargedevice, means to pass the space current of said device through saidwinding to energize the same, and means to control said space current inaccordance with the energy level 'of the sound source and an independentsource of space energy for said amplifier.

' 6. In combination, a pick-up device adapted to be actuated by a soundrecord, amplifying means actuated by said device, a utility actuated bysaid amplifying means, means to control the response characteristics ofsaid pick-up device and of said utility, and means controlled by theenergy level of said sound record to actuate said control means wherebythe response of said pick-up device and of saidutility is increased athigh energy levels 5 and vice versa.

'I. In a system of the class described, a pick-up device adapted to beactuated by a sound record, space discharge amplifying means actuated inresponse to energy translated by said pick-up nieans, a loud speakingdevice having an armature coil and a field coil, said armature coilbeing actuated by energy derived from said amplifying means, a secondspace discharge means, means controlling said second space dischargemeans in accordance with the average level of said energy and meanscontrolled by said second space discharge means for controlling theenergization of said field coil.

8. The method of reproducing sound from a sound record which comprisestranslating said record into electrical energy, amplifying saidelectrical energy, applying said amplified elec-- trical energy to aloud speaker and controlling the response characteristics of said loudspeaker in accordance with the average energy level in such a mannerthat the volume ratio of the reproduced soundwaves is altered withrespect to the indicated volume ratio of said record.

9. In combination, a first translating device having an armature windingand a field winding, a second translating device fed thereby, and meansfor energizing the field winding of said first translating deviceaccording to the energy ,from the armature winding thereof.-

10. In combination, a first translating device, a secondtranslating-device fed by said first device, a magnetic field in saidfirst translating device and means for controlling the strength of saidfield according to a moving average of the energy from said firsttranslating device.

- 11. In combination, a first translating device, a second translatingdevice fedby first device, magnetic fields in both said translatingdevices and racweans for controlling the strength of said fields rdingto a moving average of the energy from said first translating device.

JOHN HAYS HAM'MOND, JR.

